DESCRIPTION: Drosophila telomeres are formed of long tandem arrays of two non-LTR retrotransposons, HeT-A and TART. The studies described in this proposal focus on the protein products of the genes encoded by the HeT-A and TART elements. They will test the hypothesis that products of the HeT-A and TART gag genes are key to understanding how these two elements are targeted specifically to telomeres and thus give important information on the maintenance of chromosome ends. HeT-A and TART are also models for understanding the gag gene that makes up nearly half the genome of the typical non-LTR retrotransposon (and all of the genome of HeT-A). HeT-A offers an exceptionally favorable model for study of non-LTR retroelements because it is expressed at relatively high levels. The dual nature of these elements makes study of their proteins doubly informative. The studies proposed involve 1) yeast two hybrid experiments to screen for interactions between relevant combinations of HeT-A gag proteins, TART gag proteins, and TART reverse transcriptase to determine whether they are capable of forming particles by either homomultimerization or heteromultimerization: 2) RNA binding experiments looking for interactions between HeT-A and/or TART RNA and proteins encoded by these elements to form ribonucleoprotein particles (RNP) we have identified; 3) cell fractionation to isolate such RNAs; 4) antibody studies to identify relevant proteins both in cytological preparations and in cell fractions; 5) yeast two-hybrid screens for proteins interacting with HeT-A and TART proteins to identify proteins, perhaps chromosomal end proteins that might be involved in targeting these elements to telomeres.